1. Field of the Invention
The present invention relates generally to a suspension device which can be used to support vibrating bodies on a base and more specifically to such a suspension device which can be used to attenuate the transmission of vibration between an automotive power unit and a vehicle chassis, particularly during idling modes of power unit operation.
2. Description of the Prior Art
JP-A-60-104828 discloses a previously proposed suspension device which is designed to support a power unit (engine/transmission unit) on a vehicle chassis. This device includes an elastomeric body in which main and auxiliary working chambers are defined. The chambers are connected by an orifice passage structure in which electrodes are disposed. The chambers and the passage structure are filled with an ERF (electrorheological fluid) which undergoes an increase in viscosity when exposed to a high voltage. When the elastomeric body is distorted by the movement of the power unit, the volume of the main working chamber changes, which tends to pump ERF back and forth to the auxiliary chamber.
By impressing a high voltage on the electrodes in response to the engine rotational speed (by way of example), it is possible to control the viscosity of the slug of ERF in the orifice passage structure and thus control the dynamic spring constant and the vibration transmission phase in a manner which enables vibration damping in a number of different frequency ranges.
However, this relatively straightforward approach to the problem of controlling vibration has room for improvement.